Human movement measurement system

ABSTRACT

A system for measuring the position of transponders for testing and training a user to manipulate the position of the transponders while being guided by interactive and sensory feedback through a bidirectional communication link to a processing system for the purpose of functional movement assessment for exercise and physical rehabilitation.

This application is a continuation of U.S. Ser. No. 11/187,373 filed 22Jul. 2005, now U.S. Pat. No. 7,292,151, issued 6 Nov. 2007, which claimsthe benefit of U.S. 60/592,092, filed 29 Jul. 2004. Each of theseapplications is incorporated by reference as if fully recited.

BACKGROUND OF THE ART AND SUMMARY OF THE INVENTION

This invention relates to a system and methods for setup and measuringthe position and orientation (pose) of transponders. More specifically,for training the user to manipulate the pose of the transponders througha movement trajectory, while guided by interactive and sensory feedbackmeans, for the purposes of functional movement assessment for exercise,and physical medicine and rehabilitation.

Known are commercial tracking and display systems that employ eithersingularly, or a hybrid fusion thereof, mechanical, inertial, acousticalor electromagnetic radiation sensors to determine a mobile object'sposition and orientation, referred to collectively as pose.

The various commercial tracking systems are broadly classified by theirrelative or absolute position tracking capability, in which system thepose of a mobile object is measured relative to a fixed coordinatesystem associated with either combination of receiver(s) or passive oractive transmitter(s) housing mounted on the user. The tracking system'scomponents may be tethered with obvious inherent movement restrictions,or use wireless communication means to remotely transmit and process theinformation and allow for greater mobility and range of movement.

Typically these tracking systems are utilized for biomechanics and gaitanalysis, motion capture, or performance animation and require thesensors to be precisely mounted on the joints. Various means ofpresenting the tracking information in a visual display are employed,such as Heads-Up Display (HUD), that provide occluded or see-throughvisibility of the physical world, or Fixed-Surface Display (FSD), suchas computer desktop monitors, depending upon the simulation andimmersive quality required for the application. The application mayrequire various degrees of aural, visual, and tactile simulationfidelity and construct direct or composite camera views of the augmentedor three dimensional (3D) virtual reality environment to elicitinteractive user locomotion and/or object manipulation to enhance theuser's performance and perception therein. The tracked object may berepresented in the virtual environment in various forms, i.e., as afully articulated anthropoid or depicted as a less complex graphicalprimitive. The rendering strategy employed depends upon the degree ofphoto realism required with consideration to its computational cost andthe application's proprioception requirements.

Tracking technologies possess certain inherent strengths and limitationsdependent upon technology, human factors, and environment that needconsideration when discussing their performance metrics. Regardless ofdifferentiating resolution and accuracy performance benchmarks, manyimplementations suffer from varying degrees of static and dynamicerrors, including spatial distortion, jitter, stability, latency, orovershoot from prediction algorithms. Some human factors includeperceptual stability and task performance transparency, which are moresubjective in nature. And environmental issues such as line-of-sight,sensor attachment, range, and multiple-object recognition, need to beconsidered when selecting the optimal technology for the most robustapplication development. Irrespective of the intrinsic strengths andweaknesses of the tracking technology employed, ultimately the user'ssatisfaction with the system's utilization and efficacy, including theproduction of reliable, easily understood, measurable outcomes, willdictate the overall success of the device.

This invention's system and methods facilitates biomechanical trackingand analysis of functional movement. In the preferred embodiment, thisinvention is low cost, robust, easy to deploy, noninvasive, unobtrusive,and conveys intuitive and succinct information to the user to executemovement properly and provides performance indicators of said movementfor feedback purposes. One feature of the present invention provides foran interactive tracking system because the sensor functionality, orreferred to herein as active transponders or transponders, is integratedwith local user input control, and real-time sensory interfaces on thesame device. The transponder is a wireless communication and monitoringdevice that receives a specific signal and automatically responds with aspecific reply. In one embodiment, the invention provides functionalmovement assessment based upon the relative measures of limb pose withrespect to two positions defined by the transponders. The transponderscan operate independently or work in unison to process and sharecomputational tasks and information between the local databases. Thisdecentralized, distributed processing scheme allows the configurationand coordination of the training session, and processing and analysis ofthe measurements to occur without requiring expensive auxiliary computerand display systems to manage the same, and without relying on costlysoftware development of complex synthetic environments for visualizationpurposes. Also, the user can manage the applications and performancedatabases off-line on a remote computer system with Internetconnectivity to customize and configure the system parameters in advanceof their session.

The present invention is designed to provide such system and methods forhigh-fidelity tracking or registration of the poses of activetransponders and engage the user to purposely manipulate thetransponders' pose along a prescribed or choreographed movementtrajectory in order to train and assess functional movement capability.In the preferred embodiment, the system is comprised of two subsystems:(1) a subsystem comprised of one or more active transponders, which, inits most sophisticated implementation, responds to periodic requestsfrom another component of the system to radiate or transmit a signal forpurposes of absolute position tracking; processes an embedded inertialsensor for relative orientation tracking and absolute trackingrefinement; and provides an essentially real-time aural, visual, andtactile sensory interfaces to the user, and (2) a subsystem comprised ofa centralized position processor system or unit and receiverconstellation unit, collectively referred to as the processor unit,which is essentially a signal processor that synchronizes thetransponders' periodicity of radiating signal and other operationalstates; collectively receives and processes the radiated signal;iteratively calculates the transponders instantaneous pose andconvolution, thereof; and continually exchanges this information, andits analysis thereof, with the transponders and/or auxiliary hostcomputer system in essentially real-time via a combined wireless andtethered communication means. This real-time bi-directional exchange ofinformation allows for proper transponder identification, coordination,and the accurate measurement of pose, thereof, and timely actuation ofthe sensory interfaces for optimal user regulated closed-loop control.

The transponder is broadly classified by its level of hardware andsoftware configuration that define its scope of intelligence, sensorysupport, and configuration. The degree of intelligence is determined byits capability to locally access, process, and modify the database.Further, either transponder classification can be sub-classified by itsmanipulative requirements. In one embodiment, where multipletransponders are used, a principle transponder is consciously anddeliberately moved along the reference movement trajectory, while asubordinate transponder serves as an anchor or secondary reference pointelsewhere on the locomotion system whose kinematics are not necessarilycontrolled by the user's volition.

An interactive transponder, preferably, has significant intelligence;supports relative and absolute tracking capabilities; provides completesensory stimuli support; provides for functional enhancement throughattachment of modular, extension pieces; and provides a user display andinput system to control the training session. In the preferredembodiment, the interactive transponder is primarily held in the hand tofacilitate more complex user input and greater sensory intimacy.Conversely, in another embodiment, the fixed transponder has limitedintelligence; supports only the absolute pose tracking capability;provides no sensory stimuli support; and is usually mounted to a fixedsite on the limb or trunk.

A combination of transponder deployment strategies may be requireddepending on the training session's objectives, such as two interactivetransponders grasped by each hand; or alternatively, an interactivetransponder, and a fixed transponder attached to the limb or trunk; orlastly, two fixed transponders attached to the limb(s) and/or trunk.

In one embodiment, this invention proposes to elicit movement strategiesbased on the deployment of at least two transponders that define theendpoints of a movement vector whose relative translation and rotationis measured and evaluated for the assessment of functional movementcapability, including but not limited to, limb range of motion and itscontrol thereof, limb strength conditioning, and overall proprioceptionand hand-eye coordination skills, and overall body movement. Thisregistration system measures a single movement vector whose endpointsare comprised of an anchor point, i.e. one that is located in a lessdynamic frame of reference, e.g., such as the trunk or abdomen, andanother more distal location fixed on or held by a limb or extremity,e.g., the hand, arm, or leg. As this movement vector is translated androtated through space by the act of the user modifying the pose of theprinciple transponder in concert with the reference movement trajectory,the vector's length will expand and contract relative to the proximityof principle transponder with respect to the subordinate transponder.The vector's length conveys unique and explicit information regardingthe user's movement efficiency and biomechanical leverage. For example,by attaching a fixed subordinate transponder at the hips and a fixedprinciple transponder on the upper arm, the biomechanics of the act oflifting a box or similar object can be elegantly qualified. If the userassumes a poor lifting technique, i.e. legs locked with the trunkseverely flexed with head down and the arms stretched out beyond thebasis of support, the vector's length would consistently be measuredlonger than compared to a good lifting technique, i.e., legs bent atknees with the back straight, head gaze up, and arms close to body.Also, the measurement(s) of higher-order derivatives derived fromnumerical mathematical processes of a reference point described by thevector would provide additional indication of movement control orsmoothness. In summary, one embodiment of the present invention iscomprised of:

a means to create a single movement vector whose endpoints are definedby the locations of at least two transponders, wherein, the expansionand contraction of the vector's length is calculated, analyzed, andreported in essentially real-time;

a means to create a single movement vector whose endpoints are definedby the locations of two transponders, wherein, a representative pointalong the vector length is referenced and its higher-order derivativesare computed by mathematical numerical processes, wherein the result iscalculated, analyzed, and reported in essentially real-time; and,

a means to correlate said vector's length and at least one other measureconsisting of a higher-order derivative, to the reference movementtrajectory, wherein the result is calculated, analyzed, and reported inessentially real-time.

A registration system for practical functional movement applicationsshould clearly convey information to the user regarding his movementquality while he performs the task, without compromising or distractingfrom said execution by unnecessary head movements or change in eye gazeand normal focus. Poor visualization strategies that distract the userare ineffectual for promoting heads-up, immersive interaction, and thealphanumerical information it imparts often can not be consciouslyprocessed fast enough to elicit corrective action. This system providesfor both a local, standalone sensory interface as a primary feedbackaid, or alternatively, an interface to a remote fixed-surface displayfor greater visualization and simulation capabilities. The visualstimulus could be modulated to warn of range violations, or providesignals for purposes of movement cadence and directional cueing. Aprinciple interactive transponder is typically hand-held, which isnaturally in close proximity to the user's aural and visual sensoryfield during most upper extremity movements, or, conversely, the visualstimulus may be viewed through a mirrored or reflective means if not inoptimal line-of-sight. A remote fixed-surface display might augment theimmersive quality of the user's experience by providing control of aview camera of a simulated computer environment, and display of thetransponders and/or interactive objects' static or dynamic poses withinthe computer display's skewed through-the-window perspective projection.

In summary, one embodiment of the present invention is comprised of:

a means for modulating an embedded luminescent display organized andoriented into a directional-aiding pattern, by varying its degree ofintensity and color, or other physical characteristics, to provide avisual display stimulus. This sensory interface is excited at a rate,repetition, or pattern proportional to the pose error of thetransponders' movement trajectory compared to the reference movementtrajectory;

a means to view said visual display stimulus with the aid of a mirror(s)or other reflective means;

a means for the real-time projection of sound or speech commands throughan audio device to provide warning, alarm, instructional, andmotivational aid, and/or additional cueing upon encroachment of staticand dynamic limit/boundary conditions defined by the reference movementtrajectory;

a means for real-time tactile feedback including, but not limited to,modulation of the rotational properties of a vibrator motor proportionalto the pose error of the transponders' movement vector compared to thereference movement trajectory;

a means for combining the excitation of said stimuli proportional to thepose error of the transponders' movement vector compared to thereference movement trajectory; and,

a means to coordinate the real-time, periodic parametric update andmodulation of the stimuli imparted by the sensory interfaces within thetransponders from a processing unit by means of a wireless communicationlink.

This invention addresses the need for an intuitive, interactive methodto instruct, create, and deliver a movement trajectory command withoutnecessarily relying on pre-programmed, regimented movement trajectories.The registration system can be configured via remote setup at theprinciple transponder to pre-record and choreograph a free-form movementtrajectory of the principle transponder with the intent of the usermimicking the same said path. This impromptu learning modality canexpedite the session down time between different users and movementscenarios, and accommodate users' high anthropometric variability inrange of movement. In summary, one embodiment of the present inventionis comprised of:

a means is to provide a movement trajectory learning modality thatallows the user to calibrate and create the desired endpoints,midpoints, and/or total reference movement trajectory through userprogrammer entry of an input device resident on the transponder;

a means to process and save a movement trajectory using acomputationally efficient Catmull-Rom spline algorithm or other similarpath optimizing algorithms to create control points along key points ofthe movement trajectory that define the optimally smoothest pathintersecting the control points;

a means to provide database management by a processing unit via awireless communication link or, alternatively, through user data entryof an input device resident on the interactive transponder; and,

a means to access, edit, and store the program and/or databases tononvolatile memory operably coupled to the principle transponders forthe purpose of automating the creation, delivery, storage, andprocessing of movement trajectories. Customized user programs anddatabases would be downloaded from a central repository or relevantwebsite in advance of the training session to the transponder from theuser's home location via the Internet or other convenient locales havingnetworked Internet access, and transported to the systems remotephysical location, and uploaded into the system's memory, and executedas the application program.

This a priori process of remote selection, download, and transfer ofprogrammatic content and database would minimize the user's decisionmaking and input during product utilization by offering only relevantand customized programming material of their choosing targeted for theirspecific exercise, fitness, or rehabilitation goals. Performance datacould be saved indefinitely in the database's nonvolatile memory, untilan upload process was performed through the said network so the databasecould be transferred to another location for purposes of, but notlimited to, registration, processing, archival, and normativeperformance evaluation, etc.

An exemplary list of specific data structures contributing to oraffecting the means for automating the creation, delivery, storage, andprocessing of movement trajectories described below may be stored withinthe non-volatile memory of the transponder or position processor whichmay use high-density serial FLASH, although other types of memory may beused such as SmartMedia, Compact Flash, etc. Additionally, the memorydevice interface should not be limited to internal, but may includeexternal media devices, such as USB FLASH Key or other portable mediameans, that may have inter-operability with other computerized devices.The data structures may include:

Modulation & Feedback Thresholds/Triggers Properties—the aural, visual,tactile interfaces require threshold settings which determine theirexcitation or stimulation characteristics. These settings can be derivedfrom previous performance data or defaults determined from normativedata, or modified in real-time, by algorithmic methods including movingaverages, standard deviations, interpolation based upon goal-orientedobjectives, etc.

Normative Performance—performance data collected over a large populationof users through controlled studies, that is distilled down intospecific user categories based upon certain demographics that the usermay compare and rank his/her results. This data may be initiallyembedded within the transponders or position processor non-volatilememory and may be augmented or modified automatically or by uservolition when connected to the Internet.

Competitive Ranking—applications which have a predominate pointgoal-oriented purpose would allow access to a global ranking filearchive accessed through the Internet or automatically via updatedexecutive files. This ranking file would be created through an analysisof user participation and publishing of his/her results through InternetWeb-based services.

Downloadable Executive Programs & Configurations—new software programs,including new features, enhancements, bug fixes, adjustments, etc.,could be downloaded to the transponder through an Internet connection.Graphics images would be stored in compressed or uncompressed binaryforms, i.e., bitmap, gif, jpeg, etc. This new programs could betransferred to any suitable computerized position processor unit locatedat a remote facility via the transponder's wireless link. Therefore, theuser's transponder is the node that establishes the portable networkcapabilities of the system, not necessarily the computerized positionprocessor.

Custom Menu Interfaces—specialized activities may require more advanced(or simplified) interfaces dependent upon the users' cognitive abilitiesand interactive specificity. This menu may include interactive queriesor solicit information regarding the user's daily goals, subjectiveopinions or overall impression of the activity and ones performancewhich could be incorporated in the Motivation Index described below.

Report Generation Tools and Templates—XML, HTML or other authoringlanguage used to create documents on the Web that would provide aninteractive browser-based user interface to access additionalperformance data analysis and report generation tools and templates thatmay not be available or offered with the standard product.

Custom Performance Algorithms—certain application-specific performanceanalysis may require dynamically linked algorithms that process andcalculate non-standard or specialized information, values, units,physical measurements, statistical results, predictive behaviors,filtering, numerical analysis including differentiation and integration,convolution and correlation, linear algebraic matrices operations tocompute data pose and scaling transformation, and proprietary types. Oneexample of a proprietary type is Motivation Index, a composite numericalvalue derived from a weighted average of statistical performanceindicators and subjective user input including relative scoringimprovements, conformity to ROM pattern, lengthy activity accessduration, high access rate, relative skill level improvement, daily goalachievement, etc., that could represent the overall level of enthusiasmand satisfaction, the user has for a particular activity.

Range of Motion (ROM) Pattern Generator—the ROM pattern requires somekey control points to be captured along the desired trajectory andstored in order that the algorithm can calculate an optimally smoothpath, in real-time, during the comparative analysis phase.

ROM Pattern Capture & Replay—the ROM pattern can be can saved to memoryin real-time by discrete position samples versus time depending upon theresolution desired and memory limitations and later played back on thetransponder or remote display for analysis.

Activity Specific Attributes—includes Reps/Sets, Duration, Pause, HeartRate Limits, intra-activity delay, level, point scalars, energyexpenditure, task-oriented triggers, etc., and other parametric datathat controls intensity, execution rate and scoring criteria for theactivity.

Instructional Information—textual, graphical, or animation-basedinstruction, advice, coaching, activity description, diagramedtransponder deployment and intra-device connectivity, etc. thatfacilitates the intuitiveness, understanding, and usage of the system.The form of instruction may include music files saved in variousformats, including Wave, MP3 or other current or future audio datacompression formats, and video files saved in MPEG or other current orfuture video data compression formats.

Real-time Data Management—proprietary data management protocols thatreside above the communication driver layer that manage the real-time,synchronous and asynchronous exchange of data between transponder(s) andposition processor. This would provide an essential real-time sharing ofactivity data, analysis, and feedback stimulus thresholds, orcoordination of multiple transponder configurations, or for acollaboration of same or different user requirements to complete asimilar activity objective.

This invention addresses the need for adaptability of the registrationsystem to different movement measurement scenarios. In one embodiment,it utilizes a versatile, modular configuration and mounting of thetransponders onto the user. The efficient deployment of the transducersbetween different users' and from task to task requires a universalmounting scheme to provide consistent localization and pose of thetransponders at the desired measurement sites on user's body. Also, tocompensate for the receivers' finite tracking volume when stationary,the receiver constellation unit may be mechanically modified to optimizeits tracking properties by conveniently repositioning it in closerproximity to the expected transponders movement trajectories andline-of-sight, thereof. In summary, one embodiment of the presentinvention is comprised of:

a means to quickly and efficiently alter the location of thetransponders using a fastening system designed to quickly attach anddispose various forms of transponder assemblies;

a means to augment the physical properties, i.e., weight and length, ofthe principle transponder with adjunct electro-mechanical componentsthat provide variations in biomechanical leverage for isotonic andisometric utilization; and,

a means to allow the user to manually alter the geometry and pose of thereceiver constellation unit to facilitate an optimal tracking locationbased upon collectively maximizing the ultrasonic source's energyreceived at the transducer interface.

This invention addresses the practicality and robustness of theregistration system when used in either indoor or outdoor environments,and especially when the tracking volume likely contains potentiallyoccluding objects, i.e., an uninvolved limbs or clothing, that becomepotential sources of competing, reflected paths. The preferredembodiment of the registration system utilizes the time of flight (TOF)measurement of ultrasonic acoustic waves due to its immunity frominterference from the visible and near-visible electromagnetic spectrumand its superior ability to overcome most multi-path reflectionsproblems by simple gated timing of the initial wave front. Upon commandfrom the processor unit, the transponders produce a few cycles burst ofultrasonic energy and the transducers of the receiver constellation unitare stimulated and mechanically resonate accordingly, upon the wavefront arrival. The processor unit's analog signal processing circuitstransform the mechanical energy into electrical signals that resembletapered sinusoidal waveforms, which another electronic circuit triggersupon using an adaptive threshold technique which, in turn, the processorunit detects and calculates TOF timestamps indicating the wave frontarrival. In the preferred embodiment, the system overcomes theultrasonic technology's intrinsic challenge of precisely triggering onsame the waveform location and provides consistent unambiguous triggerdetection by complementing the adaptive threshold technique with asoftware timestamp correction algorithm, which includes in part, adigital over-sampling and averaging timestamp algorithm, a relativetimestamp correction scheme utilizing a predictive algorithm ofhigher-order Taylor series based derivatives, and an absolute timestampcorrection scheme that minimizes the range error based upon discretebiasing of timestamps.

Further, in the preferred embodiment, the processor unit utilizes theabsolute and relative trigger timestamps in a multi-modal trilaterationalgorithm for the measurement of three-dimensional (3D) translations androtations of the transponders. The primary trilateration calculation isderived by an application of Pythagoream theorem involving a pointposition solution based-upon range measurements from at least three (3)points, versus the well-known triangulation method which uses bearingangles of two cameras of known pose. Additionally, the system's mainaccuracy limitation is mostly affected by the temperature variability ofoutdoor environments and its influence on the speed of sound in airvalue. This algorithm mitigates this problem by mathematically computingthe speed of sound every analysis period provided at least five (5)receivers and a transponder synchronizing means are utilized. If theintegrity of the synchronizing signal is temporarily compromised, thesystem automatically employs a variation of the trilateration algorithmthat uses the last known speed of sound value.

In the preferred embodiment, the maximum update rate, and hence themajor contributor to the latency of the position calculation, isdetermined by the typical acoustical reverberation, typically between 20to 100 ms, encountered in an indoor environment. Since the transpondersare held or fixed on the user's body and, therefore, are mobile, the TOFmeasurements will experience an additional latency effect. A Kalmanfilter is used as a prediction/estimation strategy to minimize andcompensate for the latency effect. The prediction algorithm uses ahigher-order Taylor series based derivatives and augmentative inertialsensor data. Its predictive refinement is dependent upon predefinedmodels of expected movement conditions. Because functional movement isepisodic, having periods of stillness interspersed with bursts of motionactivity, a multi-modal filtering strategy is preferably employed tohandle the unpredictable jerkiness at the start of motion and relativelypredictable, smooth motion afterwards. In summary, the preferredembodiment of the present invention is comprised of:

a means to detect the same carrier wave cycle of ultrasonic energy usinga software correction algorithm requiring multiple, consecutive TOFacquisitions as input for the digital over-sampling and averagingalgorithm, the calculation of a higher-order numerical differentiationof the past and current TOF information as input for the predictivealgorithm of higher-order Taylor series based derivatives used for therelative TOF correction, and a measurement of the intra-pulse timeintervals of consecutive TOF acquisitions as input for the absolute TOFcorrection scheme that minimizes the range error based upon selectivebiasing of the TOFs;

a means to utilize a dual matrix formulation of the trilaterationalgorithm, and a calculation strategy thereof, which decision isdependent upon the integrity of the system's communication link,synchronization condition, and the desired measurement accuracy; and,

a means to coordinate the information transfer between transponders andthe processor unit so that their contribution to the resultant movementvector calculation can be measured without intra-signal interference.

These goals will be attained by such system and methods that arecomprised of the user's interaction described by the following steps asset forth as the preferred embodiment:

-   -   a. Authenticate user access and open user session from a local        or remote database;    -   b. Setup user training session, i.e., workload limitations,        measurement criteria, and audio/visual/tactile stimuli;    -   c. Select training program and configure its options;    -   d. Deploy the transponders as instructed to predefined locations        of users locomotion system to create at least one transponder        movement vector;    -   e. Calibrate the transponder movement vector to establish its        reference pose;    -   f. Create a movement trajectory using learn mode, if required;    -   g. Initiate the start of session;    -   h. Determine the instantaneous pose of transponder movement        vector relative to its reference pose from a periodic temporal        iteration of this step;    -   i. Perform qualitative and quantitative statistical analysis of        accumulated measured poses of the transponder movement vector        relative to the pattern of instantaneous poses defined by the        reference movement trajectory;    -   j. Update the major transponders sensory interfaces to modulate        said system parameters in a periodic temporal iteration of this        step;    -   k. End the session once program objectives have been obtained;    -   l. Analyze the results by interacting with local and/or remote        databases;    -   m. Provide numerical, graphical, and/or animated information        indicating desired performance measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments will be better understood when reference ismade to the accompanying drawings, wherein identical parts areidentified with identical reference numbers and wherein:

FIG. 1A illustrates one example of a deployment apparatus of the presentinvention;

FIG. 1B illustrates one example of hand-held form for the transponder ofthe present invention;

FIGS. 2A-2D illustrate example extension pieces for the presentinvention;

FIGS. 3A-3D illustrate one example of process flows for the presentinvention;

FIGS. 4A and 4B illustrate a sample application of the presentinvention;

FIG. 5 illustrates a block diagram of the remote processing system ofthe present invention;

FIGS. 6A-6C illustrate example receiver configurations of the presentinvention; and

FIG. 7 illustrates a block diagram of the components of one embodimentof the transponder of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention provides a practical, versatile measurement toolfor the assessment of the user's manipulation strategy of thetransponder 10 or transponders along a reference movement trajectory.Moreover, the system and methods measure and analyze the kinematics ofthe relative translations and rotations of the limbs or extremities withrespect to each other or to a more inertial reference location on or offbody as the transponders are manipulated. This information providesuseful insight on biomechanical demands and anthropometric factors thatinfluence human movement efficiency and control. Although measurementperformance metrics are important design criteria, it's equallyimportant to provide intuitive and motivating program instruction andadministration, and to provide comprehensive analysis and integration ofthe motion data in a form that is objective and easily interpreted. Thissystem improves upon the practicality and user interactive aspects ofsetup, deployment, calibration, execution, feedback, and datainterpretation of a tracking system designed for function humanmovement.

Human movement is a response to external environmental forces whichrequires the accurate coordination of the distal segment(s) tocompensate for these forces. Skillful coordination of human movement isdependent upon the cohesive interaction of multiple sensory systems,including visual, vestibular, with the musculoskeletal system. Morespecifically, the challenges and goals of cognitive spatial mapping, (2)minimization of energy expenditure, (3) maintaining stability, (4)steering and accommodation strategies for various environments, (5)dynamic equilibrium, (6) active propulsion and weight support, and (7)core locomotion pattern should be relationally considered to properlyassess human movement. Therefore, it is preferable to engage theinteraction of these sensory systems during a training session topromote the desired functional movement outcome. Because many movementspersist for 400-500 ms, enough time is allowed for the initiation of themovement and for user correction based upon visual and kinestheticinformation acquired during the time of the movement. However, theimplemented means of visual feedback should be not be distracting orinterfering with the task at hand. In the preferred embodiment, thissystem engages the sensory systems with non-distracting, intuitive,embedded aural, visual, and tactile stimuli which provide real-timeindication of the principle transponder pose error with respect to thereference movement trajectory.

In order to conduct a time efficient training session, this registrationsystem attempts to minimize the encumbering experimental setup andcalibration procedures characteristic of more complex and higher costmotion analysis technology. These complementary systems serve importantacademic or clinical oriented research needs or for motion capture forcomputer animation purposes and strive for highly accurate measurementof joint motion data in terms of angular displacement. Therefore, theintegrity and reliability of their motion data is dependent upon propersensor setup and calibration.

For instance, single axis goniometer-based systems usually requirespecially designed harnesses to hold the monitor and are firmly strappedor taped over the joint to avoid relative motion artifacts. Usuallythese devices are tethered and their fit, weight, and constrainingmechanical linkages can impose limitations on the joint motion and causediscomfort for the user. Most optical or video-based systems require theplacement of numerous active or passive markers over landmarks, such asthe joints' center of rotation. These systems should guaranteesufficient environmental illumination and contrast between markers andbackground to function optimally. Also, these systems are severelyaffected by occluded markers that may disappear for long periods of timedue to rotations and line-of-sight limitations. Other video-basedsystems do not use markers but require the assignment of the body'sjoints manually or through computerized automation during data analysis,making real-time analysis arduous and real-time feedback virtuallyimpossible.

In the preferred embodiment, the system doesn't require complicated,time consuming sensor setup and calibration by virtue of it minimalistsensor requirements and uncomplicated sensor mounting. Instead, itrequires only the deployment of a sensor on the body (in one embodimenta dual sensor group on a combination of limb(s) and or trunk) anddoesn't enforce stringent movement protocol, but encourages free-form,unrestrictive movement of the transponders.

The transponder's preferred deployment means, include either insertioninto a universal strap and holster apparatus (FIG. 1A) that secures onthe user's limb, extremity, or trunk, including, but not limited to, thehip, ankle, knee, wrist, upper arm, neck, waist or an augmentativemechanical attachment to one or a combination of modular extensionpieces shaped into a hand-held form (FIG. 1B). A strap or torx-like clipand holster design provides a firm, yet light weight and comfortablemounting location away from areas that clothing and or uninvolved limbsmay occlude.

The modular extension piece is either an instrumented sensory typedesigned to support alternative tactile stimulus device or alternativeconfigurations of aural, visual, and tactile feedback types, ornon-instrumented, weighted extension pieces as shown in FIGS. 2A-2D. Allmodular extension pieces may be of various physical dimensions andintrinsic weight, with a captive handle design that preferably requireszero grip strength to grasp. Alternatively, the modular extension piecemay be coupled to the transponder through a fixed or flexible,segmented, articulated coupling to accommodate attachment of additionaltransponders and/or other modular extension pieces. These componentswould quickly assemble to each other using a spherical snap joint ortwist snap latch, or similar mechanism, to provide quick alteration ofform and function when used for different movement trajectory scenarios.

In one embodiment, the weighted extension attachments (FIG. 2A) areoffered in fixed gradations of one (1) kilogram increments or otherconvenient unit of measure and either be indicated as such with anumerical label, quantitative mark, or color-code feature, orcombination thereof. For upper extremity evaluation, the weightedextension piece integrated into a zero-grip handle would enhance theimprovement of musculature strength of the limb, while not compromisingthe user's endurance with a potentially fatiguing hand grasprequirement.

In one embodiment (FIG. 2B), the tactile type provides force feedbackfunctionality by controlling the rotational speed of an embeddedvibrator motor in the shaft. Alternatively, the visual type (FIG. 2C)may be comprised of a series of light emitting diodes that could beuniformly embedded along the length of the handle or transponder andtheir intensities variably controlled therein. It should be appreciatedthat a simple, economical mirrored or reflective surface placed in frontof the user's visual field could provide sufficient real-time indicationof the user's subjective conformity to the said movement trajectorywhile allowing non-distracting viewing of this visual stimulus. Forexample, a program that requires the user to reposition the principleinteractive transponder through an arc-like movement trajectory in themidsagittal plane through out a range of motion beginning from the waistupwards until parallel to shoulder height. As the user performs themovement, the visual sensory interface could be proportionally excitedif the user moves too quickly, or hesitates too long, or produces shakyor erratic episodic motions, or is beyond the prescribed bounds of themovement arc. The light stimulus is easily viewed in the mirror andwould indicate corrective action in his or her movement strategy, whileappropriate aural commands may be issued simultaneously to encourage thesame correction. Regardless of the sensory interface type, its controland excitation properties will be determined by some statistical aspectof the user's conformity to and progression through the movementtrajectory.

The hand-held transponder may include a modular extension piece with anembedded graphic display device and associated input means to allow theuser to setup, operate, provide visual feedback, and view performanceresults of the device usage without additional remote display means.More specifically, a software-controlled user interface could providecertain visual prompts in a menu oriented presentation, to instruct theuser on (1) device setup, i.e., aural, visual, and tactile feedbackparameters, types of program start and termination cues, programintensity based on ratio of amount of repetitions, sets, and restperiods or categorical gradation of challenge, learn mode behavior,etc., (2) scrollable program selection with brief descriptions includingobjective, desired measurement, i.e., range of motion, energy, accuracy,speed, etc., and instructive information, and (3) alphanumeric and/orgraphical display of measured performance data and other biophysicaldata and its analysis thereof, displayed in standard plotted formsincluding line, bar, and pie charts, etc. It is important to note thatthe user input process is intuitive and streamlined so as not to detractfrom the practicality and user friendliness of the system. Only relevantapplications and its control thereof will be sequestered from thedatabase and presented to the user.

In one embodiment, two or more transponders and extension pieces, orcombinations thereof, may be assembled at their endpoints with auniversal spring coupling. The assembled device could be grasped in bothhands and bent in various rotational angles about the spring coupling'saxis. Isotonic strength conditioning programs can be developed due tothe force resistance feedback supplied by the spring. Amulti-transponder assembly in the form of a flexible rod or staff couldprovide an indication of balance of upper extremity strength andproprioceptive function dependent upon the angular closure rate androtational imbalance and orientation deviation from initial startingposition.

Additionally, in the preferred embodiment, the modular extension pieceshave provisions for other attachable apparatus (FIG. 2D) that canaugment the program's intensity or difficulty. For example, an eyelet isembedded in the end of the extension piece and is designed to attach anelastomeric band, such as the type manufactured by Theraband®. Bysecuring the other open stirrup end of the band to the user's foot,isotonic strength conditioning programs can be developed due to theforce resistance feedback supplied by the elastomeric band. Moving thetransponder through a movement trajectory is now made more restrictiveand challenging.

APPLICATION EXAMPLES

An example training session deploying a dual transponder group is nowdescribed that may be designed to improve the range of motion, strength,and coordination of shoulder abduction in a user. The training sessionwould primarily serve as an exercise aid that provides essentialfeedback to the user so that he/she learns to progressively improve themanipulation of the transponder through the reference movementtrajectory, while benefiting from increased shoulder range of motion andstrength improvement.

In advance of the training session, a software application is operatedfrom a host computer that provides a utility for baseline configurationand management of the system's and transponder's local databases, and/oraccess to other remote databases, and for the real-time interface to thedata flow between the system's components. The application's navigationand selections are presented to the user through a typical graphicaluser interface like Microsoft Windows® XP operating system. Ageneralized step-wise procedure requires the administrator or user to(1) select the desired program and features from a menu screen list, and(2) to initiate a communication process that causes the programparameters to be transferred to the processor unit through a standardcomputer communication protocol, i.e. serial, USB, ethernet, etc.,whereupon, (3) the information is subsequently processed and transferredinto the transponders local memory via a wireless communication link,and, finally, (4) the transponder's software program accesses thisdatabase to manage the device utilization and configuration of the localdisplay means. Alternatively, a Compact FLASH-based memory card,embedded serial FLASH, or a similar nonvolatile memory device providesthe user an additional specialized database supporting remote datacollection capabilities. This database would be preprogrammed in advanceand the resultant performance data retained, even if the device's poweris lost, or for extended unsupervised exercise sessions conductedremotely from the host computer system or when the host computer systemis unattached or unavailable. After the session is completed, the userwould be queried if the results are to be saved for later analysis orwould automatically be saved, dependent upon device setup. This datacould be retrieved at a later time when the system is once againattached to a host computer system, and the software utility could becommanded to upload the database.

Henceforth, the following procedural description refers to the activitydependencies diagrammed in FIGS. 3A-3D that the user would encounterwhile operating the system.

During the Security Phase (FIG. 3A), the user may be requested toprovide a security authentication code for validation, which opensaccess to his/hers custom programs in the training session. Next, duringthe Setup Phase (FIG. 3A), the user can configure global options orselect the desired program. The global options may include, but are notlimited to, workload intensity, measurement criteria, sensory interfaceproperties, and reporting features. A program menu list would indicatename, ID, and a brief description, or alternatively, be represented by adetailed graphical icon. When the program is selected, otherprogram-specific options can be setup.

During the Deployment Phase (FIG. 3B), and dependent upon the program'sobjectives, a suitable combination of transponder types will be mountedon the user's body as instructed by the program. This example requiresthe assembly of a hand-held interactive transponder with graphicaldisplay, and a weighted extension piece coupled therein to be grasped bythe hand on the same side as the affected shoulder. Another subordinatetransponder 12 is placed into a holster assembly strapped around thelower quadriceps on the same side. This setup is shown in FIG. 4.

During the Calibration Phase (FIG. 3C), a simple calibration proceduremay be requested to evaluate transponder function and specific userrange of motion constraints. Typically, this information is determinedbeforehand and saved in the system's database. Also, practicality ofthis system is claimed for lack of extensive calibration requirements.

Dependent upon the program's options, a user-defined movement trajectorymay be created prior to program start in lieu of executing thepredefined version. The learn mode could be utilized to quicklychoreograph free-form movement trajectories and save them into thetransponder's non-volatile memory for later execution. The learn modewould be accessed through the user interface and instruct the managementof the control point assignment by pressing the push button switch atthe appropriate junctures of movement discontinuity or, preferably,allowing automated assignment by the software. In the preferredembodiment, a computationally efficient Catmull-Rom spline is used todefine a three dimensional (3D) curve that passes through all thecontrol points along the movement trajectory path. If manuallyinterceding, the user is instructed to press the push button once ateach major juncture in the movement trajectory, but, preferably, for nomore than a few locations, until the desired end of range of motion isreached as shown in FIG. 4B. Similarly, the return path may be similarlydefined or he/she may elect to use the same forward path in reverse.These control points are registered by the processor unit andtransferred and saved to the transponders' memory to serve as thecontrol points for the real-time calculation of a Catmull-Rom spline.The Catmull-Rom spline is calculated in real-time from the desiredinitial starting point to provide a continuous set of position pointsrepresenting the “learned” reference movement trajectory.

After the program is selected or the learn mode complete, the user maybe instructed to alter the pose of the transponders to satisfy theinitial starting conditions of the program. Either one or a combinationof sensory interfaces could be excited by the principle transponder tocause the user to direct or steer it towards the desired start point.For instance, the visual sensory interface could sequentially extinguishor dim its peripheral light sources to converge to a central lightsource as the principle transponder is positioned closer to the desiredstart point. Alternatively, the aural sensory interface could change itstonality and loudness as the start point is approached. Oralternatively, the tactile sensory interface could be modulated toprovide less force feedback as the start point is approached.

During the Execution Phase (FIG. 3D), the transponders are continuallymanipulated along the reference movement trajectory to the best of theuser's skill and fidelity, within the bounds of the user's physicallimitation, until an aural, visual, or tactile response is given thatindicates the activity volume has been successfully completed or asufficient number of conformity violations or failures have beenregistered. The processor unit calculates the instantaneous posecoordinates of the transponders every analysis interval and periodicallycommunicates this information to the transponders via the wirelesscommunication link. As the principle transponder is moved in mimicry tothe reference movement trajectory the conformity error between theactual and reference movement trajectory is calculated periodically inreal-time to determine the characteristics of feedback quality to beelicited by the sensory interfaces for the user's closed-loop control tocorrect his/her manipulation strategy. For example, the conformity errormay be calculated from statistical processes based upon the standarddeviation of the least mean squared (LSM) principle transponder'sposition error compared to the reference movement trajectory, or basedupon, or combination thereof, a threshold magnitude of some multi-ordernumerical differentiation of said movement to indicate a “smoothness”quality of translation and rotation along the movement trajectory path.

Alternatively, a host computer system could provide an auxiliaryprocessing and display means to allow another software program to accessthe transponder's calculated positional data through an applicationprogrammer's interface and use this data to alter the pose of agraphical primitive in proportion to the motions of the transponderswithin the context of computer generated virtual environment. Thedynamic control of objects in the computer generated virtual environmentcould be used to augment the local sensory interfaces of thetransponders through an interactive, goal-oriented video game modality.The video game challenges could be increased over time based upon somescoring criteria of successful manipulation of the principallycontrolled on-screen graphical object with respect to cueing derivedfrom other secondary static or dynamically moving objects. It isimportant to note that only primitive forms of video game challengeswould be considered, to take into account the user's cognitive awarenessand physical limitations, and the economics of software development forphoto realistic virtual environments and animation. Also, this auxiliarycomputer display means would offer an alternative visualization methodof interactive and immersive video feedback aid to enhance theapplication presentation.

Additional examples of how the present invention may be applied aredescribed as follows:

Balance

The body has the ability to maintain balance under both static anddynamic conditions. In static conditions, such as in standing, the bodystrives to efficiently maintain posture (often referred to as posturalstability) with minimal movement. In dynamic conditions such as inwalking or sports play, the body strives to maintain balance whileperforming in an ever changing environment. The ability to maintainbalance is a complex process that depends on three major sensorycomponents. The sensory systems include visual, vestibular andproprioception. For example, we rely on our visual system (eyes) to tellus if the environment around us is moving or still; we rely on ourvestibular system (inner ears) to tell us if we are upright or leaning,standing still or moving; and we rely on our proprioceptive system (feetand joints) to tell us if the surface we are standing on is uneven ormoving. If balance problems develop, they can cause profound disruptionsin your daily life. In addition to increased risk for falls, balancedisorders can shorten attention span, disrupt normal sleep patterns,cause excessive fatigue, increase dependence on others and reducequality of life. It is not uncommon for individuals with a history ofbalance problems to regain their balance control through accuratediagnosis followed by specific medical treatment and/or rehabilitationexercises.

The present invention described can be used as a testing and trainingdevice for balance improvement under both static and dynamic conditions.

One testing and training scenario for postural stability would be tomeasure frequency and amplitude of body sway in three dimension (3D)space while feet remain in a fixed position. This task can be performedin both a double or single leg stance to test for bilateral symmetryrelating to balance. Another modification of the test would be toperform each test with eyes both open and closed to help determine thecontribution of the visual component to overall balance ability.Tracking body sway while creating the illusion of motion through propervisual cueing on a display means would be another test to help determinethe reliance on specific sensory components of balance. Deliveringrepetition of protocols with increasing difficult oscillation thresholdswith biofeedback of successes and failures of such predetermined goalsis one way to train to improve balance.

The transponder can deliver aural, visual, and tactile stimuli to queuethe individual to the degree of frequency and amplitude of bodyoscillations. The aural and tactile components provide the only means offeedback when the testing and training are performed with eyes closed orthe visual field is compromised. Examples include, but are not limitedto, (1) an audio signal increasing and decreasing in volume proportionalto the amplitude of body sway, (2) a vibration action proportional tofrequency of body oscillations, and (3) a light source illuminated whenboth frequency and amplitude goals are achieved. Multiple transponderscan be used to evaluate and reinforce proper balance posture bycommunicating position information of certain body segments inrelationship to others. An example would be the comparison of positionof the head with respect to the hips while generating a vibration actionif an excessive forward lean of the head as compared to the hips isrecognized.

Another test for balance would be to test ones Limits of Stability(LOS). This test refers to ones ability to effectively operate withintheir sway envelope. The sway envelope or LOS is defined as the maximalangle a person's body can achieve from vertical without losing balance.An individual with healthy balance is capable of leaning (swaying)within a known sway envelope and recover back to a centered positionwithout the need for a secondary maneuver such as a step, excessive bendat the torso or arm swinging. LOS for bilateral stance in normal adultsis 8 degrees anterior, 4 degrees posterior and 8 degrees laterally inboth directions.

The present invention described can be used as a testing and trainingdevice for balance control during movement or perturbations within adesired sway envelope. Through proper visual queuing represented on thedisplay means that defines a normal sway envelope, the amount of bodydisplacement can be measured from vertical stance.

The transponder can deliver aural, visual, and tactile stimuli to queuethe individual as to when he or she has achieved the desired range oftheir sway envelope, then assess the individual's ability to return backto a vertical stance. Examples include, but are not limited to, (1) avibration action when the user varies (meanders) from the desiredmovement path, (2) an array of lights change intensity and pattern asthe individual successfully approaches the intended target, (3) an audiosignal is generated when the individual has maintained a stable positionwith respect to proper visual queuing represented on the display meansfor a selected period of time. Multiple transponders can be used toevaluate and reinforce proper balance posture by communicating positioninformation of certain body segments in relationship to others. Anexample would be the comparison of position of the head with respect tothe hips while generating a vibration action if an excessive forwardlean of the head as compared to the hips is recognized.

Dynamic balance can be evaluated while having the individual performcoordinated movements which specifically challenge the variouscomponents of balance in a dynamic nature. Such movements include, butare not limited to jumping, hopping, and walking. These movements can beperformed with eyes both open and closed, during interaction with staticor dynamic visual queuing on the display means. The ability to performthese dynamic balance tasks with comparisons to others of similar sex,age or disability can be assessed. Example measurements may include, butare not limited to, (1) amount of body sway in three dimension (3D)space, (2) time to complete specific task, and (3) effects of fatigue onbalance ability.

Balance training in both static and dynamic conditions can be easilyachieved by providing specific visual queuing on the display means,which challenge the individual to perform repetitive and progressivelymore difficult balance drills. Performance reports can be generated toestablish a baseline, isolate specific strengths and weaknesses withinthe specific sensory and motor control aspects of balance, and documentprogression and improvements.

The transponder can deliver aural, visual, and tactile stimuli to queuethe individual as to when he or she has achieved the desired balancetask. By example, a vibration action is produced proportional to thefrequency of a body segment oscillation after the user lands from a hoptest and attempts to stabilize and maintain proper postural balance.When the individual finally stabilizes and achieves correct posturalbalance, an audio signal indicates the task has successfully completed.Multiple transponders can be used to evaluate and reinforce properbalance posture by communicating position information of certain bodysegments in relationship to others. An example would be the comparisonof position of the head with respect to the hips while generating avibration action if an excessive forward lean of the head as compared tothe hips is recognized.

Range of Motion (ROM)

The present invention described can be used as a testing and trainingdevice to determine the range of motion within a joint. Range of Motionis the normal distance and direction through which a joint can move.Limited ROM is a relative term indicating that a specific joint or bodypart cannot move through its normal and full ROM. Motion may be limitedby a mechanical problem within the joint that prevents it from movingbeyond a certain point, by swelling of tissue around the joint, byspasticity of the muscles, or by pain. Diseases that prevent a jointfrom fully extending, over time may produce contracture deformities,causing permanent inability to extend the joint beyond a certain fixedposition.

The present invention described can be used to test the starting pointand end point which an individual is capable of moving a body part,typically a limb and associated joint(s). Comparisons to age and sexbased normative data can be made. Proper visual queuing can berepresented on the display means to instruct and motivate the individualthrough the proper testing procedure.

The present invention described can be used as a testing and trainingdevice for individuals involved in physical rehabilitation or generalfitness to improve ROM. Proper visual queuing can be represented on adisplay means to motivate individuals to extend their range of motionbeyond their current capabilities.

The transponder can deliver aural, visual, and tactile feedback thatalerts the individual to successes or failures in proper execution ofeach repetition. An example of tactile feedback would be thetransponders are vibrated if the individual's movement trajectory variedfrom the intended two dimensional (2D) reference movement trajectory bydeviation from the planar path into the uninvolved spatial dimension. Anarray of light sources could increase illumination in intensity andrepetition as the ROM goal was approached and an audio tone could signalthe individual they have achieved the desired pause time at the properROM.

Multiple transponders can be deployed to determine the contribution ofeach joint or anatomical structure where more then one joint is involvedin the ROM movement (example; shoulder and scapular in overheadreaching). The vector sum of each transponder movement in a specificaxis can be added together to determine the total ROM. The ROM of onejoint in a two joint motion can be subtracted from the total ROM todetermine the contribution of a single joint in a two joint movement.

Human Performance Testing and Training

There are many devices that test the strength and speed of isolatedjoint movements, for example, the leg extension and bicep curl. Thisinformation has value in testing both healthy individuals, athletes andindividuals whose strength and speed capabilities may be compromised byinjury, disease, poor conditioning or simply age. Recently in the fieldof human performance, it has been recognized that the analysis of themobility of the isolated joint, although providing some value, does notoffer enough information to determine how the body will perform duringfunctional movements. Functional movements are defined as movementsequal to those encountered on the athletic field, in the workenvironment or while performing activities of daily living. Functionalmovements involve the movement and coordination of multiple joints andmuscle groups acting together to perform a more complex task then asingle, isolated joint movement.

The present invention described can be used as a testing and trainingdevice for functional movement improvement. By tracking variousregistration points on the body with respect to each other or to anoff-body registration point, performance measurements of functionalmovements can be assessed, such as jumping, cutting, turning, bounding,hopping, shuttling, etc.

The present invention described can be used as a testing and trainingdevice for individuals involved in physical rehabilitation, generalfitness or sports performance enhancement to improve their functionalmovement abilities. Proper visual queuing can be represented on thedisplay means to instruct and motivate individuals to perform specificfunctional movements.

The transponder can deliver aural, visual, and tactile feedback ofproper movement execution. Examples include, but are not limited to, (1)an audio signal alerting the user that the desired performance stance isincorrect, (2) the light sources illuminate when the desired speed isachieved in a first step quickness drill, (3) a vibration action toindicate the limits of tracking range, (4) a vibration actionproportional to the magnitude of a biophysical measurement during theinteraction with visual queues represented on the display means, (5) avibration action when the body or limb position does not correlate wellto the desired body or limb position of the visual queuing representedon the display means, (6) an audio signal indicating start, stop andpause periods or other controlling events, (7) an audio signalindicating proper body alignment or posture has been compromised, and(8) an audio signal indicating the relationship of desired target heartrate to a desired threshold.

Hardware Description

In the preferred embodiment, the processor unit is comprised principallyof a constellation of five (5) ultrasonic transducers and signalprocessing circuitry, thereof, and a signal processor that interfaces tothis receiver group, performs the pose calculations, and interfaces tothe transponders and host computer databases. The following interfacedescriptions for the processor unit are based upon the dependency flowrepresented by FIG. 5.

The sensors 14 preferably used for the receiver constellation unit arecylindrically-shaped ultrasonic transducers, for example, the modelUS40KR-01 40 kHz PVDF ultrasonic receivers manufactured by MeasurementSpecialties Inc., which provide adequate acoustic pressure sensitivityand exhibit 360 degree omnidirectional broad beam response along thehorizontal plane. The omnidirectional characteristic, albeit in oneplane only, is very desirable to minimize line-of-sight occlusion.Because of its low resonance Q value, the rising and decay times aremuch faster than conventional ceramic transmitters. This reduces itspower requirements since less burst drive duration is needed to achievesufficient triggering thresholds at the receiver. This transducer typeis also utilized similarly in the transponders to provide the potentialfor the most optimal acoustic coupling.

The receiver constellation unit is preferably mounted on a fixed supportbase, and has a pivoting and/or swiveling mechanical linkage whichprovides an adjustable mechanism for configuration of the receiverconstellation unit's inertial frame of reference relative to thetracking field. In the preferred embodiment, it is strategicallypositioned and oriented in proximity to the tracking field in order (1)to minimize line-of-sight degradation with respect to the expectedtransponder orientation, (2) to optimize registration resolution withrespect to field volume size, and (3) to satisfy the mathematicalrestrictions of performing trilateration calculations based upon thesolution of simultaneous linear equations. It should be noted that thetrilateration matrices may be solved if the matrices have a rank offive, and are non-singular, i.e., the matrix determinant is non-zero. Inthe preferred embodiment, the geometric parameters and their coordinatelocation of the receiver constellation must insure linear independenceof the columns of the matrices and to avoid the matrices from becomingsingular.

One example geometrical permutation of the receiver constellation unitthat satisfies these rules is shown in FIG. 6A. It occupies a volume ofapproximately 8 cu. ft. and essentially fixes the transducers in a waythat defines two primary orthogonal, bisecting planes defined by threenon-collinear points each. Another preferred implementation thatoccupies nearly the same volume is shown in FIG. 6B and is characterizedby its S-shaped curve and tilted with respect to the horizontal plane.Another preferred implementation that occupies nearly the same volume isshown in FIG. 6C and is characterized by its helical or logarithmicspiral shape oriented perpendicular to the horizontal plane. Further, asindicated in the preceding figures, the transducers vertical axes areoriented 90° with respect to the typical vertical axis orientation ofthe transponder's transmitter to improve acoustic coupling in thevertical plane, a consideration for overhead, upper extremity tracking.Although this causes some reduction in the lateral registration bounds,the compromise provides a more symmetric field about the middle orprimary location of tracking interest.

In the preferred embodiment, the overall size of the receiverconstellation unit is predicated on a phenomenon referred to asGeometric Dilution of Precision (GDOP). The solution of a uniquethree-dimensional location based upon trilateration requires the preciseresolution of the common intersection of multiple spheres circumscribedby the distance between each transmitter and receiver transducer. Eachsphere has an inexact radius due to system noise and measurementresolution. Therefore, the intersection becomes a volume instead of apoint and the size of the volume is dependent upon the radii of theintersecting spheres as well as the distance between the spheres'centers. As the radii get larger with respect to the distance betweenthe centers, i.e., the transmitter is farther down range, the spheresbegin to appear more and more tangential to one another and theintersection volume increases, although not necessarily symmetrical inall dimensions. Therefore, to minimize position uncertainty, thereceiver transducers should be separated from each other as much aspractical proportions allow with respect to the confines of the trackingfield volume as the above said geometric examples provide.

This receiver constellation unit can be repositioned with respect to thetracking field by a simple mechanical adjustment as shown in thepreceding figures. The mechanical adjustment raises and lowers andchanges the length and pivot axis of the cantilever arm which is fixedto a ground base support.

Because the receiver constellation unit operates a distance from theprocessor unit, each receiver preferably has an associated pre-amplifiercircuit to convert the high-input impedance piezoelectric signal into alow-level voltage proportional to the acoustic signal energy impingingthe transducers sufficient in order to accurately transmit the signalsto the processor unit. In one embodiment, a high-input impedance ACamplifier design with 30 dB gain can be utilized. The preferredoperational amplifier is the OPA373 manufactured by Texas Instruments.It was chosen for its low 1 pA input bias current, high 6 MHz GBW, andlow-voltage single supply operation. The amplifier is configured as anon-inverting type with the high-pass cutoff frequency set at 1 kHz. Theoverall circuitry is preferably enclosed in a metal shield to minimizeelectromagnetic noise coupling into the highly sensitive amplifierinputs. In addition, a local, regulated power supply is included toallow for a wide range of input voltage supply and provide sufficientpower supply rejection to compensate for the noise susceptibility ofremote power distribution. All the pre-amplifier circuits' power andsignal connections preferably originate from the processor unit.

The processor unit subsystem preferably consists of an analog signalprocessing interface that provides (1) additional voltage amplificationand filtering of base band signal from the preamplifiers, (2) absolutevalue function, (3) peak detection function, and (4) analog-to-digitalcomparator function to provide support for an adaptive threshold means.The adaptive threshold technique provides robust triggering of the mostproximal ultrasonic source at a precise temporal point along thetraversing sinusoidal waveform of the electrical signal. Essentially, anew threshold signal is recalculated each analysis period based upon asmall percentage reduction of the last peak waveform detected.Therefore, the tracking range is not necessarily restricted due to anarbitrarily high threshold setting and the noise immunity is improved asthe threshold tracks the waveform envelope and not transientdisturbances. An alternative automatic gain control strategy for theamplification function is unnecessary since the trigger threshold willadjust to the signal level instead. In the preferred embodiment, thethreshold faithfully tracks the peak to minimize integer period phaseerrors, so the amplifier's gain is set to prevent signal saturation fromoccurring when the receiver constellation unit and transponders are inclosest proximity during normal use.

In one embodiment, an amplifier and BW (band width) filter circuitreceives the output from the sensor and preamplifier circuit andprovides additional amplification and low-pass filtering to condition itfor reliable threshold triggering and input to other analog signalprocessing circuitry. A dual amplifier configuration may be used toprovide an additional gain of 40 dB, AC coupling to remove DC offsets ofthe preamplifier outputs and long cable losses, and low-pass filter toreject noise beyond the interest signal's bandwidth. The first stageamplifier may be configured as a non-inverting type with a gain of 20dB. The low-impedance DC input signal is effectively blocked by thecoupling capacitor in series at its non-inverting input with a high-passfrequency cutoff set at 20 kHz. This gain stage feeds a second amplifierconfigured as low-pass, 2^(nd) order Butterworth MFB filter. This filtertype provides smooth pass band response and reduced sensitivity tocomponent tolerances. The second stage low-pass frequency cutoff is setat 80 kHz with a pass band gain of 20 dB.

An absolute value circuit receives the output of the amplifier and BWfilter circuit and converts the bipolar signal into a unipolar form formagnitude detection. A dual amplifier configuration may be used toprovide highly accurate full wave rectification of the millivolt-levelsignal. The first stage amplifier feedback switches to control thedistribution of input current between the two signal paths dependentupon the input signal polarity. For a positive input voltage the inputcurrent will be positive which forward biases D1 and reverse biases D2.This configures the 1^(st) stage as an inverter driving the invertinginput resistor of the 2^(nd) stage, which is also configured as aninverter because its non-inverting input is held at virtual ground dueto the non-conducting path of D2. This effectively creates a combinedcircuit of two cascaded inverters for an overall gain of +1. For anegative input signal its input current is negative which forward biasesD2 and reverse biases D1. This configures the 1^(st) stage as aninverter driving the non-inverting input of the 2^(nd) stage whichchanges the sign of the circuit gain. In this mode, the input current isshared between two paths to the input of the 2^(nd) stage, where −⅔ ofthe input current flows around the 1^(st) feedback stage and −⅓ flows inthe opposite path around the 2^(nd) stage feedback path for a net gainof −1.

In the preferred embodiment, a peak detect and sample-hold circuitreceives the output of the absolute value circuit and registers a peakvalue that is required to set a magnitude threshold precisely at somepercentage of full-scale of the peak. A dual amplifier configuration maybe used to provide the highest ratio of high output slew rate to lowdroop. The first stage is typically in negative saturation until theinput voltage rises and exceeds the peak previously stored on the samplecapacitor at the inverting input. Now the amplifier acts as a unity gainbuffer and the input voltage charges the sample capacitor whichfaithfully tracks the rising voltage. Once the input voltage diminishesin magnitude, the first blocking diode reverse biases and the samplecapacitor holds an accurate replica of the highest voltage attained withminimal droop because of the low input bias current of the amplifier andelimination of leakage altogether in the second blocking diode bybootstrapping its cathode at the same potential provided by thelow-impedance buffer of the second output stage. An electronic switchand bleed resistor allow the voltage across the sample capacitor to bereset by the processor during power up and after the triggering event isrecorded so the adaptive threshold value can be refreshed each cycle. A1^(st) order Butterworth filter may be used at the input to smooth falsein-band transients that could disrupt the peak accuracy detection.

In the preferred embodiment, a comparator circuit receives the outputfrom the peak detect and sample-hold circuit to convert the analogsignal to digital form for high-speed triggering operation of theprocessor. The preferred device is the MAX941 which is manufactured byMaxim. A percentage of the peak threshold is used to set the invertinginput. When the non-inverting voltage exceeds the inverting voltage, thecomparator's output will trip and produce a high-true logic pulse thattriggers the processor. A latch control input allows the processor todisable the comparator action to prevent unnecessary triggering duringthe reverberation phase and to prevent potentially disruptive noisyoutput chattering near threshold crossover beyond its hystereticimmunity. The percentage of threshold level is predetermined through thescaling resistors to be set low enough to trigger on the rising edge ofthe signal's first crest at the furthest range of transponder operation,but high enough above the intrinsic system noise level and externalnoise caused by reverberation and other ultrasonic sources. Once thefirst crest is registered, subsequent crests may be triggered at theirzero-crossing representing the most precise timing registration bymomentarily disabling the sample-hold circuit. Because of the longerduration trigger receptivity window, early multiple reflections aremitigated by transducer placement at least 3.5 cm away from adjacentplanar surfaces, so the reflected acoustic energy doesn't produce acanceling effect of the direct acoustic energy of the later crests. Oncea sufficient number of crests have been registered, then the triggeringwindow is blanked for the remainder of the analysis period by latchingthe comparator's value.

In the preferred embodiment, a digital signal processing interface isconnected to the analog signal processing interface to transform theanalog trigger processing into digital position information.

The digital filter circuit receives output from the comparator circuitand preferably consists of a digital low-pass filter implemented in acomplex programmable logic device (CPLD) that serves to precondition thecomparator circuit's digital outputs. The preferred device is anAT1504ASVL CPLD which is manufactured by Atmel. Base band system noiseor other glitches potentially occurring in the analog signal processorinterface, but prior to the actually arrival of the ultrasonic signal,could cause a threshold disruption that registers a “runt” pulse as afalse trigger condition. The “runt” pulse would be misinterpreted as theactual TOF trigger and cause serious error in the position calculation.An AND/NOR one-hot state machine design may be used to ignore leveltransitions that are not stable for at least ½ system clock frequency×8states, so only transitions of 4 μS or greater are passed through. Thesystem clock delays introduced by the digital filter's synchronous statemachine affect all channels the same and are, therefore, effectivelyeliminated by the inherent dependency on relative measurement.

In the preferred embodiment, the processor and digital filter circuitsreceive the output from the analog processor and provide controllingsignals therein. The preferred processor circuit is the MC9S08 GB60which is manufactured by Motorola Inc. It is a low-cost,high-performance 8-bit microcontroller device that provides all theaforementioned hardware circuits integrated into one convenient device.The calculation circuit is abstracted from embedded 60 KB FLASH forprogram memory with in-circuit programmable capability and 4 KB RAM fordata memory. The time base circuit is preferably comprised of anexternal, high-noise immunity, 4.0 MHz system clock, which multipliesthis by the internal frequency-locked loop for a bus clock of 40.0 MHzand single instruction execution time of 25 ηS. This clock also providesall the capture and control timing functionality for the other specifiedcircuits. Multiple parallel I/O ports and dedicated asynchronous serialcommunication signals provide for the digital control of the analogsignal processing and communication interfaces, respectively.

The timing capture-control circuit receives the output from the digitalfilter circuit representing the arrival of the TOF triggers to determinethe relative TOF propagation of the ultrasonic acoustic wave as itpasses through the receiver constellation unit. More specifically, it iscomprised of a five channel 16-bit timer input capture module withprogrammable interrupt control that provides edge detection and 50 ηstiming precision to automatically register the TOF triggers timestampsasynchronously without using inefficient and less accurate softwarepolling means.

The phase-locked loop circuit receives the output from the timingcapture-control circuit and is preferably comprised of a three channel,16-bit timer compare module is implemented as an all-digital phaselocked loop (ADPLL), which synchronizes the capture window and blankingfunctions with respect to the reference input channel. It is comprisedprimarily of a free-running 16-bit timer configured to periodicallyinterrupt the processor dependent upon a precise convergence of itsperiod and phase to the reference trigger source, by means of anover/under count matching and correction technique.

The A/D conversion circuit receives the output from the amplifier and BWfilter circuit and consists of an eight channel 10-bit analog-to-digitalconverter used to monitor channel offsets and magnitudes for range andpolarity errors and correction. This information is utilized by thecalculation circuit as input to the TOF software correction algorithm todetermine the slope of the waveform crest.

In the preferred embodiment, the serial communication circuit iscomprised of two asynchronous serial communication interfaces that areconnected between the calculation circuit and host link and radio linkcircuits of the communication interface. The host link provides a 115Kbit per second (baud) bi-directional communication link to an auxiliaryhost computer system through a Serial-to-Universal Serial Bus bridge.The preferred device is the CP2101 which is manufactured by SiliconLaboratories. It supports the conversion of a fully asynchronous serialdata bus protocol, with buffering and handshaking support, to anintegrated Universal Serial Bus (USB) Function Controller andTransceiver and internal clock providing USB 2.0 full-speed compliancy.An integrated 512 bit EEPROM stores the required USB device descriptors,including the Vendor ID, Product ID, Serial Number, Power Descriptor,Release number and Product Description strings. A host computer mayenumerate and access this device utilizing the manufacturer's virtualCOM port device drivers using a USB channel.

In the preferred embodiment, the radio link circuit is comprised of awireless bi-directional communication interface to preferably (1)broadcast a synchronization signal to control the transpondersinteroperability, (2) to receive other transponder sensor data,including, but not limited to, accelerometer, heart rate, battery, userI/O status, (3) to provide control messages for the transponders'sensory interfaces, and (4) to provide means to configure transponders'local databases. The preferred wireless communication link is based uponthe AT86RF211, a highly integrated, low-power FSK transceiver optimizedfor license-free ISM band operations from 400 MHz to 950 MHz. andmanufactured by Atmel. It supports data rates up to 64 kbps with dataclock recovery and no Manchester Encoding required. The device has athree wire microprocessor interface that allows access of read/writeregisters to setup the frequency selection, transmission mode, poweroutput, etc. or get information about parameters such as battery, PLLlock state, etc. In normal mode, any data entering its input channel isimmediately radiated or any desired signal collected by the aerial isdemodulated and transferred to the microprocessor as reshaped registerbit information. In wake-up mode, the device periodically scans for anexpected message sequence and broadcasts an interrupt if a correctmessage is detected.

In the preferred embodiment, at least three (3) consecutive TOFtimestamps are registered for each receiver during the acquisitionphase. Preferably, the transponder's transducer emits a multi-cycleultrasonic acoustic burst of at least ten cycles in duration so thatsufficient energization of the receiver transducer is realized and atleast three crests of the waveform can be properly registered. At lowsignal levels when ultrasonic acoustic coupling is poor, thisrequirement may fail and an invalid tracking status is asserted.Preferably, the reference receiver transducer of the receiverconstellation unit is positioned in closest proximity to the acousticsignal source so that it is the first transducer to be affected by theinitial wave front. This reference receiver provides the overall systemtiming and state machine control for the phase-locked loop circuit, sothat the processing, calculation, and communication tasks are executedin a deterministic and efficient fashion.

It should be appreciated that a high-resolution ultrasonic acoustictracking system that depends upon threshold detection means has aninherent uncertain trigger dilemma. This uncertainty arises because ofthe multi-cycle nature of the transmitted signal's waveform and theassociated difficulty detecting the exact temporal location forconsecutive analysis periods when the signal's magnitude may varygreatly depending upon the efficiency of the acoustic coupling, thedistance between transmitter and receiver, and signal-to-noise ratio ofthe signal processing techniques. If a threshold is set near one of theminor crests of the waveform during the last analysis period, then it isconceivable a slight reduction of magnitude of the waveform during thenext analysis period may fall slightly below the set threshold andactually not be triggered until the next larger excursion of thewaveform occurs. This would create a TOF error proportional to theperiod of the acoustic waveform or its intra-pulse interval and have adetrimental affect on the measurement accuracy. This analog processingdescribed above establishes trigger thresholds that allow no more than asingle intra-pulse interval of uncertainty, but that is still inadequatefor high-resolution measurements. Although a technique is known thatcontrols the largest peak profile of the transmitter acoustic signal andclaims to provide an absolute trigger condition, this procedure isdifficult to reliably tune and control among different transducer types.

In the preferred embodiment of the invention, no modulation of theacoustic signal is required. Rather, the adaptive threshold method isaugmented with a TOF software correction algorithm that unambiguouslydetermines the correct TOF based upon a means to detect the same carrierwave cycle of ultrasonic energy every period. The software correctionalgorithm requires multiple, consecutive TOF acquisitions as input forthe digital over-sampling and averaging algorithm, the calculation of ahigher-order numerical differentiation of the past and current TOFinformation as input for the predictive algorithm of higher-order Taylorseries based derivatives used for the relative TOF correction, and ameasurement of the intra-pulse time intervals of consecutive TOFacquisitions as input for the absolute TOF correction scheme thatminimizes the range error based upon selective biasing of the TOFs.

The calculation circuit preferably processes multiple, consecutive TOFacquisitions to effectively improve the timing resolution thatproportionally affects position accuracy and precision. The digitalfilter discussed above introduces quantization errors because of itsdiscrete operation. And minor fluctuations in the acoustical couplingproduces timing jitter or uncertainty in the triggered zero-crossings ofthe acoustic sinusoidal. A Gaussian average or mean value of multipleTOF is a simple and effective filter strategy. Due to the possibility ofpoor acoustic coupling or misalignment, and distant transponder locationfrom the processor unit, the number of detectable triggeredzero-crossings may vary for a fixed duration of multi-cycle ultrasonicacoustic burst. The averaging algorithm automatically adjusts to thiscondition by only including TOFs whose delta changes fall within theexpected range of the nominal intra-pulse interval defined by thetransmission properties of the acoustic source. The nominal intra-pulseinterval is determined and utilized by the following compensationschemes.

The calculation circuit preferably processes a relative TOF correctionalgorithm based upon a predictive tuned algorithm that requireshigher-order numerical differentiation calculation of the past andcurrent TOFs. This compensates the TOFs that may have registered oneintra-pulse interval earlier or later than the nominally expected timedue to the trigger dilemma described above. By formulating thesederivatives into a truncated 2^(nd) order Taylor series expansion andweighting the terms contribution, an estimate of expected TOF iscalculated and compared to the actual TOF through an iterative errorminimization calculation. A minimized error that results in a delta timechange indicative of a discrete intra-pulse interval increase ordecrease due to an early or late TOF, respectively, produces acharacteristic value that directs the algorithm to compensate the actualTOF by the intra-pulse interval and restore it to its correct value. Inthe preferred embodiment, this relative compensation algorithm worksmost effectively when, (1) the maximally expected inter-period TOFchange is less than the discrete intra-pulse interval, (2) the TOFinter-period processing is contiguous, (3) the TOF increase or decreaseis no more than a single intra-pulse interval, and (3) the Taylor seriesterms are suitably weighted in the prediction algorithm.

The calculation circuit preferably processes an absolute TOF correctionalgorithm at least once initially, when the phase-locked loop is stable,but may be performed every analysis period depending on computationalresources, that determines the initial set of TOF values for therelative correction algorithm. The initial condition that precedes thestart of the relative compensation algorithm may be due to theresumption of a stable, locked tracking state after recovery from afault condition and, therefore, requires computation of a set ofreference TOFs producing minimum range error as a starting basis. Thealgorithm utilizes a wireless synchronization means to determine areference TOF calculation between the transponder and reference sensorof the receiver constellation. By computing the reference range distanceby the product of the reference TOF and speed of sound in air, thisreference range may be compared to the range calculated from thematrices solutions described below. By iteratively and sequentialincreasing and decreasing the TOFs by a single intra-pulse time intervaland applying the input to matrices formulations described below, allpossible combinations of compensation are permutated and tested, whichproduces a unique set of TOFs that minimize the error between thecalculated range distance with respect to the reference range distance.This unique set of initial TOFs serves as the starting basis for therelative compensation algorithm. In the preferred, embodiment, thisabsolute compensation algorithm works most effectively when (1) thewireless synchronization means is tightly coupled to the excitation ofthe acoustic source, (2) the synchronizing signal's arrival is timed bythe same mechanism that times the arrival of the reference transducer'sacoustic signal, and (3) the coordinate locations of the sensors of thereceiver constellation are established to a high degree of accuracy.

The calculation circuit preferably employs two software methods oftrilateration calculation to estimate transponder position, wherein theparticular method used depends upon the availability of a synchronizingsignal and the accuracy desired. The first method is based on a relativeTOF calculation and the speed of sound is treated as a constantestimated at ambient indoor room temperature. The second method requirescalculation of an additional TOF timestamp between the transponder andreference receiver, but calculates the speed of sound as an unknownevery analysis period, and thus improves measurement accuracy. The firstmethod eliminates the global system timing variances and delays due tothe multiplicity of signal conditioning circuitry and eliminates theneed for a controlling signal means synchronized at the generation ofthe transmission of the ultrasonic acoustic wave. The second method alsoemploys relative TOF calculation but requires an additionalsynchronization signal from the processor unit to determine the absoluteTOF between transponder and reference receiver. Since the absolute TOFis based upon a single channel only, its timing latencies can be readilyaccounted for and easily corrected. This method computes the speed ofsound every analysis period, provided the synchronization signal isdetected, without need for additional hardware temperature processing orrequiring more then five (5) receivers, and automatically accounts forthe system's main accuracy limitation of speed of sound in air asdefined by Eq. 1.1, if uncorrected, yields a 1.6 mm/m ranging error forevery 1° C. temperature shift. If the synchronization signal is notdetected and, therefore, the second method is not resolvable, the lastcalculated speed of sound can be utilized within the first method'scalculation to minimize error.

(1.1)

The TOF timestamps and speed of sound values are input into linearindependent algebraic equations in a matrix formulation to solve for theunknown transponder(s) position, in a form as shown in Eq. 2.1,

(2.1)

To solve for the unknowns X, Eq. 2.1 is rearranged as shown in Eq. 3.1,whereas the inverse of A requires computation of the cofactor matrixA^(c) for the adjoint and determinant calculations for Eq. 3.2 and Eq.3.3, respectively,

(3.1)

(3.2)

(3.3)

To setup the coefficient matrix A, the utilization of five (5) receiversproduces the following set of relative TOF equations defined by Eqs.4.1-4,ΔT ₁₂ =T ₂ −T ₁  (4.1)ΔT ₁₃ =T ₃ −T ₁  (4.2)ΔT ₁₄ =T ₄ −T ₁  (4.3)ΔT ₁₅ =T ₅ −T ₁  (4.4)

The receiver locations are fixed within the system's inertial referenceframe, while the transponder(s) are mobile with respect to the samereference frame and are defined as follows,

Since each receiver is fixed at a distance D_(i) from the transponder asdetermined by the receiver constellation geometry and because theacoustic waves propagate spherically, by using Pythagorean's theorem thefollowing set of range equations are defined in Eqs. 5.1-5,

(5.1)

(5.2)

(5.3)

(5.4)

(5.5)

Equivocally, the four (4) non-reference receivers are preferably locatedat an incremental distance relative to the reference receiver, so bysubstitution of the incremental distance defined by Eq. 6.1, thefollowing set of relativistic range equations are defined by Eqs. 6.2-5,

(6.1)

(6.2)

(6.3)

(6.4)

(6.5)

By expanding and rearranging the terms of Eqs. 6.2-5, a set of fourlinear algebraic equations and four unknowns for the first methodalgorithm, depicted in the matrix form of Eq. 2.1, is defined by Eq.7.1,

(7.1)

(7.2)

Alternatively, if the second method algorithm is used, the unknown rangeof the reference receiver D₁ can be substituted by Eq. 8.1,

(8.1)

And, by rearranging terms, it is depicted in the matrix form defined byEq. 9.1,

(9.1)

Although similar results may be obtained by application of morecomputational efficient processes such as pivotal condensation orCrout's decomposition, the application of Cramer's rule was used toevaluate the first-order determinant in Eq. 3.3 using second-orderdeterminants from Laplace expansion. The final transponder(s) positionequations are defined by Eqs. 10.1-8.

(10.1)

(10.2)

(10.3)

(10.4)

(10.5)

(10.6)

(10.7)

(10.8)

If the first method is used, D, the range of the transponder to thereference receiver from Eq. 10.4 may be calculated as a redundantconfirmation of the Eqs. 10.1-3 calculations, provided the frame ofreference origin and location of the reference receiver are identical ortheir offsets accounted for. If the second method is used, C, the speedof sound in air, from Eq. 10.4 must be computed every analysis period ifits value is anticipated to be used in the first method in the absenceof a synchronization signal.

The orientation of the transponders can be derived from a similarutilization of the above algorithms for a transponder configured with atriad of ultrasonic transmitters. The transducers are preferablyarranged in a triangular plane at the transponder of sufficient area forthe desired angular resolution. The sequential excitation of eachtransducer and subsequent calculation of position by the aforementionedmethods provides sufficient information to determine orientation by theinverse kinematic calculations of Eqs. 11.1-4, where the analysis issimplified by assuming the origin of rotations occurs about T₁ and T₁₂₃represents the initial relative position matrix from this origin andT′₁₂₃ is the transformed or forward kinematic position matrix.

(11.1)

(11.2)

(11.3)

(11.4)

By examination of the matrices element equivalency of Eqs. 11.2-3 andmanipulation of terms so that the angles may be found using the inversetangent function, the following rotation equations Eqs. 12.1-3 arederived,

(12.1)

(12.2)

(12.3)

(12.4)

(12.5)

These calculations are performed through iterative step processes whichinherit angular approximations of the preceding steps until the finaldesired angular accuracy is achieved by assuming the conditions of Eqs.12.4-5. Therefore the rotation θ_(z), roll, is first approximated by Eq.12.5; then the rotation θ_(x), pitch, is approximated by Eq. 12.1; andthen the final rotation θ_(y), yaw or turn, is approximated by Eq. 12.2.The next approximation of θ_(z) utilizes the previous value of θ_(z) inEq. 12.3 and the similar steps are preferably repeated until the desiredaccuracy is achieved. The transcendental functions may be evaluatedthrough a conventional look-up table or by a power series expansion.

Preferably, the overall analysis period duration is effectively trebleduntil the three (3) transducers' positions are calculated, which reducesthe system's frequency response and imposes an increased latency effect.Typically, robust absolute orientation processing requires morestringent line-of-sight operation and is reserved for more sensitive,less dynamic, and reduced ROM movement trajectories, e.g., balance andsway. Therefore, the latency effect is less noticeable upon thereal-time performance of the sensory interfaces.

In the preferred embodiment, the interactive hand-held transponderssupport a dual axis inertial sensor, which is operably configured toprovide tilt (pitch and roll) orientation in its horizontal mountingplane. The inertial sensor is mounted in the intended operationalhorizontal plane with respect to the systems inertial frame ofreference. Once the sensors signals has been converted to anacceleration value that varies between +/−1 g the tilt in degrees iscalculated as shown in Eqs. 13.1-2, for pitch and roll, respectively.

(13.1)

(13.2)

This outside-in ultrasonic tracking implementation, where thetransponders are mounted on the mobile object, produces inherenttemporal delays due to the finite TOF registration and calculationdelays after the transponder has already moved into a different positionbefore the measurement is complete. This overall latency period iscompensated and minimized through use of a Kalman filter data processingalgorithm to estimate the pose of the transponder by optimally andrecursively combining past history, new measurements, and a priorimodels and information. Generally speaking, the Kalman filter is adigital filter with time-varying gains that are optimally determinedthrough a stochastic dynamical model of the motion. The overall goal isto minimize filter lag while providing sufficient smoothing of themotion data.

An adaptive, multi dynamic model is developed based upon the kinematicquality of the expected movement trajectory. The predictive kinematicmodel for the Kalman filter is depicted in matrix form utilizing atruncated 2^(nd) order Taylor series expansion as below in Eqs. 14.1-2,$\begin{matrix}{\begin{bmatrix}r \\v\end{bmatrix}_{k + 1} = {{\begin{bmatrix}1 & {\Delta\quad t} \\0 & 1\end{bmatrix}\begin{bmatrix}r \\v\end{bmatrix}}_{k} + \begin{bmatrix}0 \\w\end{bmatrix}}} & (14.1) \\{\begin{bmatrix}r \\v \\a\end{bmatrix}_{k + 1} = {{\begin{bmatrix}1 & {\Delta\quad t} & {0.5\quad\Delta\quad t^{2}} \\0 & 1 & {\Delta\quad t} \\0 & 0 & 1\end{bmatrix}\begin{bmatrix}r \\v \\a\end{bmatrix}}_{k} + \begin{bmatrix}0 \\0 \\w\end{bmatrix}}} & (14.2)\end{matrix}$

The Kalman filter is now described for a single dimension, although itis utilized for prediction and smoothing for all position dimensions.The predictor stages consist of the calculation of the state and theerror covariance projection equations. The state projector equation,Eq15.1, utilizes a discrete time-sampled difference equation of rcalculated from Eq. 15.2. In other words, the numerically derivedvelocity and acceleration components of motion are linearly combinedwith the previously a priori position to estimate the new position. Thecorrector stages consist of sequential computation of the gain, updatedstate estimate, and updated error covariance equations. The a posterioristate estimate, Eq. 15.4, is based on a linear combination of theweighted measurement residual and the last state estimate.

(15.1)

(15.2)

(15.3)

(15.4)

(15.5)

The new error covariance projector, Eq. 15.2, is it's previouslycomputed value combined with the current process noise covariance,Q_(k), which is tuned by an example model derived from the measuredmotion dynamics shown in Eq. 16.1. The gain's measurement noisecovariance, R_(k), is defined as a small constant and based upon theactual static timing variance empirically measured. The smaller thisvalue the more confidence there exists in the systems' measurementcapability.

In the preferred embodiment, the product of the numerically-derived1^(st) and 2^(nd) order derivatives of the measured position scaled by afrequency dependent gain provides a computationally practical adaptivedynamic process noise estimate model. The derivative product termincreases Q_(k) proportionally for higher velocity and accelerationcomponents of motion, e.g., quick, abrupt directional changes, whicheffectively increases the gain and, therefore, means more confidenceexists in the measurement rather than the estimate. This providesfaithful, low-latency response to high-frequency motions. Conversely,the frequency scaling term decreases the predictive “overshoot”characteristic of lower power, repetitive motion, e.g. slower, cyclic,ROM trajectories, which effectively decreases the gain and, therefore,means more confidence exists in the estimate rather than themeasurement. It should be appreciated this filter implementationprovides superior tracking fidelity and comparable smoothingcharacteristics as compared to practical lengths of finite impulseresponse running-average filters and various low-orders infinite impulseresponse filters. It achieves enough predictive response to compensatefor the inherent TOF and computation latencies, while providing andcomparable smoothing properties of other filter types.

(16.1)

(16.2)

In the preferred embodiment, a three dimensional (3D) piecewise cubiccurve interpolates a movement trajectory for smoothing and reducedsample storage for greater memory efficiency. Preferably, four (4)sequential discrete control points of the n-length set of controlpoints, the sample resolution dependent upon the desired movementgranularity, and corresponding timestamp are needed to calculate inreal-time the interpolated position between any pair of control points.A Catmull-Rom spline algorithm is the preferred method in that the pathintersects the control points and would best approximate a movement thatmay have acute directional changes. The Catmull-Rom spline algorithm isdefined by Eqs. 17.1-3, where the geometry matrix G_(k) represents thematrix of three dimensional (3D) control points.

(17.1)

(17.2)

(17.3)

The μ value is normalized and represents the % value between the 2^(nd)3^(rd) control points. To calculate the interpolated value between the1^(st) and 2^(nd) or the n-1^(th) and n^(th) control points, the valueof first control point of the pair and the value of the last controlpoint pair are doubly entered into the geometry matrix, respectively.The appropriate dμ/dt is determined by the desired rate of playback ofmovement trajectory. To playback at the same rate as the recordedsession, and assuming fairly constant velocity, a timestamp should alsobe saved at each control point registration so that the μ calculation iscorrectly scaled by the delta time interval. The n-length set of controlpoints would be manually registered by the user pressing a switch orautomatically post processed by a sorting method where a control pointis registered at the tangents of the trajectory having sufficientmagnitude and/or experience sign changes which indicates discontinuousor non-monotonic movement.

The major functional interfaces of the transponder unit preferablyinclude the sensory interface, transducer interface, processor, andcommunication interface. The following descriptions of the transponderunit are based upon the dependence flow represented by FIG. 6.

The sensor interface refers to the collective support for the ultrasonictransmitter, heart rate receiver, and accelerometer circuits. Theultrasonic transmitter circuit is preferably gated by a pulse-widthmodulated (PWM) digital signal at nominally 0.8% duty cycle of the 40kHz resonant frequency, e.g., a single 250 μs pulse every analysisperiod, by the processor circuit. The radiated ultrasonic signalstrength is controlled by gating a MOSFET transistor switch at a dutycycle which optimally energizes the transducer's series resonant tankcircuit for sufficient duration. The resonant circuit's reactivecomponents include an impedance matching inductor, the transducer'sintrinsic capacitance, and a small damping resistive load. At resonance,a electrical damped sinusoidal with a potential up to ˜400 V_(pk-pk) isdeveloped across the transducer to sufficiently drive it at acousticalpower levels practical for the system's intended range of operation.Enabling a lower duty cycle control through means of a softwarealgorithm monitoring the transponders range would effectively lower thetransponders power consumption and radiate less ultrasonic acousticenergy for close range operation when signal saturation and clipping isundesirable. Conversely, a higher duty cycle control would radiategreater ultrasonic energy to compensate for less efficient, non-optimalacoustical coupling orientations of the transponder with respect to thereceiver constellation. Optionally, two additional transducers may bedriven in unison or sequentially from a different transponder assemblyto support measurement of absolute rotation about a single or multipleaxes, or provide calculated positional redundancy for certain difficultline-of-sight applications.

The heart rate receiver circuit wirelessly receives a 5 kHz heart ratesignal from a POLAR® transmitter belt. The transmitter, worn around thechest, electrically detects the heart beat and starts transmitting apulse corresponding to each heart beat. The receiver captures the signaland generates a corresponding digital pulse which is received by thetiming capture-control circuit of the processor interface. A softwarealgorithm processes the signal with known time-based averaging and anadaptive window filter techniques to remove any extraneous artifact orcorruption caused by interfering sources.

The accelerometer circuit consists of a low cost +/−1.5 g dual axisaccelerometer that can measure both dynamic, e.g. vibration, and static,e.g. gravity or tilt, acceleration. If the accelerometer is oriented soboth its axes are parallel to the earth's surface it can be used as atwo axis tilt sensor with a roll and pitch axis.

The stimuli interface circuit provides the primary visual sensoryinterface preferably comprised of a linear array of five (5) bright,white light emitting diodes (LED) and associated drivers. The preferredLED device is a CMD87 manufactured by Chicago Miniature Lamp. TheseLEDs' intensity is controlled by a white LED driver. The preferred whiteLED driver device is a MAX1570 manufactured by Maxim. The white LEDdriver provides a maximum 120 mA constant current source to each LED foroptimal uniform luminescence. The drive current can be proportionallyregulated through external pulse width modulation (PWM) means from theprocessor circuit to modulate its brightness level. Additionally, anelectronic switch is connected in series to each LED drive toindividually control its active state. By simultaneously controlling thePWM duty cycle and active state of each LED, the light strobe can appearto smoothly migrate along the linear array in spite of its discontinuousoperation.

Preferably, the stimuli interface circuit provides the primary auralstimulus by means of a 4 kHz piezo buzzer. The preferred device isSMT-3303-G manufactured by Projects Unlimited. This electro-mechanicalbuzzer requires an external transistor drive circuit and digital controlsignal gated at a rate near its resonant frequency. The buzzer inputsare connected to and controlled by PWM means from the processor circuitto provide a gross volume adjustment which is dependent upon theamplitude of the drive signal.

Additionally, the stimuli interface circuit provides the primary tactilestimulus by means of a vibrator motor. The driver for the vibrator motorenables a 120 mA DC current source to excite the motor armature. Thepreferred driver device is the MAX1748 manufactured by Maxim. Therotational speed of the motor's armature is controlled by PWM means fromthe processor circuit.

The processor circuit preferably receives input from the stimuliinterface, sensor interface, and the communication interface andprovides controlling signals therein. The preferred processor circuit isthe MC9S08 GB60 which is manufactured by Motorola Inc. It is a low-cost,high-performance 8-bit microcontroller device that integrates thespecialized hardware circuits into one convenient device. The softwarecalculation engine circuit operates from an embedded 60 KB FLASH forprogram memory with in-circuit programmable capability and 4 KB RAM fordata memory. The time base circuit is preferably comprised of anexternal, high-noise immunity, 4.0 MHz system clock, which multipliesthis value by the internal frequency-locked loop for a bus clock of 40.0MHz and single instruction execution time of 25 ηS. This clock alsoprovides all the capture and control timing requirements for the otherspecified circuits. Multiple parallel I/O ports and dedicatedasynchronous serial communication signals provide digital control forthe circuits of the parallel/serial I/O circuit.

In the preferred embodiment, the graphic LCD and touch screen circuit isthe primary user input device for database management for an interactivetransponder configuration. For example, it may be a 128×64 graphicalliquid crystal display system (LCD) and associated 4-pin touch screeninput device. A preferred LCD device is the 51553 manufactured by Optrexand the preferred touch screen device is the TSG-51 manufactured byApollo Displays. LCD display information, configuration commands, andbitmaps images can be loaded through the software calculation engine viaa parallel memory interface to emulate a graphical user interface. Atouch screen input device is connected to a controller circuit to decodesoft key presses at areas over the graphical object. Preferably, the keypresses are registered, filtered, decoded, and processed by thecontroller and then transferred to the software calculation engine viaan interrupt driven asynchronous serial communication channel of the I/Ointerface. A preferred LCD controller is the UR7HCTS manufactured bySemtech.

The timing capture-control circuit provides controlling means for thestimuli interface and portions of the sensor interface. The stimuliinterface is preferably comprised of a five channel 16-bit timer PWMmodule with programmable interrupt control which provides 250 ηs timingresolution to automatically modulate the circuits' drivers throughvariable duty cycle control.

In the preferred embodiment, the A/D conversion circuit receives theoutput from the accelerometer circuit and consists of a two channel10-bit analog-to-digital converter used determine the rotational angleof roll and pitch in the accelerometer deviates from its horizontalplane orientation. This information is communicated to the signalprocessor via the radio link.

In the preferred embodiment, the radio link circuit is comprised of awireless bi-directional communication interface (with a receiver andtransmitter shown generally at 20 and 30) to (1) receive asynchronization signal for control of the transponders interoperability,(2) to transfer acquired local sensor data, including, but not limitedto, accelerometer, heart rate, battery, user I/O status, to processorunit and (3) to provide means to configure its local database fromcommand of processor unit. The preferred wireless communication link isbased upon the AT86RF211, a highly integrated, low-power FSK transceiveroptimized for license-free ISM band operations from 400 MHz to 950 MHz.and manufactured by Atmel. Its key features are described above.

In the preferred embodiment, the switch I/O circuit uses a SPST pushbutton switch for user input to control the system's operational states,start and stop program execution, and function as feedback input to theprogram. A preferred device is the KSS231 SPST pushbutton switchmanufactured by ITT Industries.

1. A system for tracking position of a user, comprising: a firstcommunication device, adapted for being attached to, or held by, theuser, comprising: a transmitter for transmitting signals; a receiver forreceiving signals; and an output device; and a processing system, remotefrom the first communication device, for wirelessly receiving thesignals transmitted by the transmitter, determining position informationfor the first communication device and sending data signals to thereceiver to provide feedback or control data to the user; wherein thefirst communication device receives and processes the received datasignals and generates sensory stimuli for the user, based on thereceived data signals and delivered through the output device.
 2. Thesystem of claim 1, further comprising: a second communication device, inelectrical communication with the first communication device and inwireless communication with the processing system, and adapted for beingattached to, or held by, the user; wherein the processing system isremote from the second communication device and is adapted fordetermining the position of the second communication device relative toat least one of the first communication device and the processingsystem.
 3. The system of claim 1, wherein: the first communicationdevice comprises a user input device adapted for communication with theprocessing system through the transmitter.
 4. The system of claim 3,wherein: the user input device is adapted for calibrating the firstcommunication device to establish a reference position.
 5. The system ofclaim 1, wherein: the processing system is adapted to determineacceleration information of the first communication device.
 6. Thesystem of claim 1, wherein: the sensory stimuli are at least one of:aural, visual or tactile.
 7. The system of claim 1, wherein: theprocessing system determines position information without interferencefrom occluding objects.
 8. An apparatus for use in conjunction with aremote processing system for tracking position of a user, comprising: atransmitter for transmitting position information signals to the remoteprocessing system; a receiver for receiving feedback or control datasignals wirelessly from the remote processing system, the data signalsderived from processed signals from the transmitter; and an output unitfor delivering sensory stimuli to the user, based upon the data signals.9. The apparatus of claim 8, wherein: the data signals are derived bycomparing the position information transmitted to reference positioninformation.
 10. The apparatus of claim 8, further comprising: a firstand a second communication device, each adapted for being attached to,or held by, the user; and each of the communication devices is incommunicative contact with the processing system directly or through theother communication device.
 11. The apparatus of claim 10, furthercomprising: a user input device deployed on at least one of thecommunication devices and adapted for communication with the processingsystem through the transmitter.
 12. The apparatus of claim 8, furthercomprising: an interactive interface such that movement of the apparatuscontrols the movement of an object in a computer generated virtualenvironment.
 13. A method for tracking position of a user, comprisingthe steps of: providing a system according to claim 1; establishing awireless communication between the first communication device and theprocessing system; exchanging data signals between the firstcommunication device and the processing system, the first communicationdevice sending position information data signals to the processingsystem and the processing system sending feedback or control datasignals to the first communication device; and providing sensory stimulito the user through the output device, the sensory stimuli based uponthe received feedback or control data signals.
 14. The method of claim13, wherein: the system further comprises a user input device adaptedfor communication with the processing system through the transmitter;and the step of exchanging data signals further comprises sending userinput data signals to the processing system.
 15. A system for trackingmovement of a user, comprising: a first communication device, adaptedfor being attached to, or held by, the user, comprising: a transmitterfor transmitting signals; a receiver for receiving signals; and anoutput device; and a processing system, remote from the firstcommunication device, for wirelessly receiving the signals transmittedby the transmitter, determining position information for the firstcommunication device and sending data signals to the receiver to providefeedback or control data to the user; wherein the first communicationdevice receives and processes the received data signals and generatessensory stimuli for the user, based on the received data signals anddelivered through the output device.